DIRECTIONS:

Whisk together all the mayo ingredients in a small bowl until well-combined. Refrigerate while you prepare the rest of the sandwich.

Lay a dish towel down on a flat surface, then place the eggplant slices, in one layer, on top. Sprinkle liberally with salt. Let rest for 10-15 minutes. This pulls out any bitterness the eggplant might have. Place the eggplant in a colander, and rinse well with cool water.

Preheat a grill to medium-high.

In a large bowl, toss together the eggplant, zucchini, yellow squash, and red onion. Drizzle with 2 tablespoons olive oil and the oregano. Toss to coat. Transfer to a grill basket.

Brush both sides of the mushrooms caps with an additional tablespoon of olive oil. Season with salt and pepper.

Place the grill basket and the mushroom caps on the preheated grill. Cook the mushrooms for 4-5 minutes, until they begin to release their moisture, then flip and cook an additional 3-4 minutes. Remove from the grill and slice thinly.

Stir the veggies frequently and grill until they are tender, about 10 minutes. If you have any larger pieces, you may wish to remove them from the basket and cook them directly on the grill (I usually do this with eggplant). Once tender, remove from grill.

Brush both sides of the bread with the remaining olive oil, grill each slice for a minute on each side until just toasted. Remove from grill.

To assemble the sandwiches, spread the mayo on a slice of toasted bread. Layer with a single layer of each veggie. Spread mayo on another slice, and place on top.